铅笔：石墨
A．毛笔：羊毛
B．碗：筷子
C．鞋：鞋带
D．稀饭：水
参考答案：D
解析： 石墨是铅笔的必须组成部分，D项符合此关系。
____ several times, the young scientist still kept on doing his experiments.
A．Having failed
B．Having been failed
C．Failed
D．To fail
简述集装箱的定义。
